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Experimental investigations into edge performance and its implications for stone artefact reduction modelling
Journal of Archaeological Science 35 (2008) 2164e2170 http://www.elsevier.com/locate/jas
Experimental investigations into edge performance and its implications for stone artefact reduction modelling Sophie Collins* Department of Archaeology and Natural History, Research School of Pacific and Asian Studies, Australian National University, Coombs Building 9, Fellows Road, ACT 0200, Australia Received 28 November 2007; received in revised form 21 January 2008; accepted 22 January 2008
Abstract This paper details an experimental investigation into stone artefact performance and use, and examines the implications for maintenance and rejuvenation activities. Controlled experiments testing the performance of differently shaped working edges reveal that rates of use attrition are not constant; they are dependent upon the blank morphology’s suitability to particular tasks. The evidence contributes to a broader understanding of the principles of reduction analyses by showing that morphological differences in blanks are accompanied by differences in the artefacts’ functional capacity. These differences in turn affect the rate at which maintenance and rejuvenation activities will be required and therefore the extent of reduction exhibited at discard. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Lithics; Experimentation; Performance; Use; Reduction
1. Reduction analysis Lithic technologists emphasise the reductive process as a means of understanding technological variability in the archaeological record (Villa, 1983; Dibble, 1984, 1987, 1995; Van Peer, 1992; Hiscock, 1993, 1994b, 1996a,b, 2006; Boe¨da, 1995; Shott, 1996; Bisson, 2000; Bleed, 1996, 2001; Hiscock and Attenbrow, 2002; Clarkson, 2002a). The processes of edge rejuvenation and maintenance in stone artefacts result in the essential properties of size, mass and form changing and reducing with successive rejuvenation events (Shott and Weedman, 2006). In most cases, the morphology of an artefact at discard is argued to indicate the amount of reduction the artefact has sustained, with some forms represented by earlier stages of reduction and others by more intensively reduced forms along a continuum of reduction (e.g. Goodyear, 1974; Jelinek, 1976; Villa, 1983; Baulmer, 1888; Hiscock, 1994b; Dibble, 1984, 1987, 1995; Hoffman, 1985; Flenniken and * Tel.: þ61 414306762. E-mail address: [email protected] 0305-4403/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2008.01.017
Raymond, 1986; Holdaway et al., 1996; Hiscock and Attenbrow, 2002). Substantial work has now been done on both the development of accurate measures of reduction (e.g. Shott and Ballenger, 2007; Hiscock and Clarkson, 2005, 2007; Shott and Weedman, 2006; Jefferies, 1990; Kuhn, 1990) and the characterisation of reduction sequences for artefact classes found all over the world (e.g. Australia, Hiscock and Veth, 1991; Hiscock, 1993, 1994a, 1998, 2003; Clarkson, 2002a; Hiscock and Attenbrow, 2002; Libya, Hiscock, 1996b; south west Asia, Neeley and Barton, 1994; Japan, Bleed, 1996, 2002; Yugoslavia, Baumler, 1888; North America, Goodyear, 1974; Hoffman, 1985; Morrow, 1997; Israel, Marks and Volkman, 1983; Gordon, 1993; McPherron, 2003; Egypt, van Peer 1992; Europe, Bietta and Grimaldi, 1990e1991; Italy, Kuhn, 1992; and in particular France, Villa, 1983; Dibble, 1984, 1987, 1995; Rolland and Dibble, 1990; Kuhn, 1995a; Holdaway et al., 1996). However, while quantifying amounts of reduction has received some attention, the idea that different shaped blanks and different types of reduction may be accompanied by different rates of use and therefore different rates of reduction, is yet to be examined.
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This paper explores this aspect of reduction by describing the results of controlled experimentation showing how artefact use influences edge rejuvenation on three blank morphologies. Artefact function is intimately related to retouch by dictating the point at which retouch/resharpening is required and whether or not it is necessary at all. The greater the amount of work an edge is able to sustain, the lower the frequency of retouch required, and the longer its use life. Data on the effectiveness of various functional edges in performing particular tasks is therefore necessary to allow some understanding of how much use may be reflected by a particular stage of reduction. The goal of this paper is to determine whether different blank forms have different performance characteristics; which would in turn imply that artefact reduction rates are influenced both by blank form and use rates. The idea of retouch as resharpening necessarily equates retouch with use; the more heavily an artefact has been reduced, the greater the amount of use attributed to it. This point has been illustrated by many studies calculating the reduction sequences for traditional archaeological ‘types,’ in which the type of each class of artefact represented at discard is argued to be subject to the amount of reduction the artefact has sustained e through use (e.g. North American and Australian projectile point typologies, Ahler, 1971; Hoffman, 1985; Hiscock, 1994b; Flenniken and Raymond, 1986; bifacial handaxes, Jones, 1994; McPherron, 1995, 1999; notched tools, Holdaway et al., 1996; and additional scraper types, Shott, 1995; Morrow, 1997; Clarkson, 2002b, 2005). Importantly, in order to allow comparisons between different artefact morphologies and the amount of reduction evidenced, the relationship between use and retouch is assumed to be fixed. This has allowed artefacts exhibiting equivalent amounts of retouch to be attributed with similar amounts of use and means the technologist need only identify reduction intensity at a site to also understand use intensity. Rates of use and reduction are assumed to be constant; however this constancy is yet to be demonstrated, representing a gap in the knowledge required for making reliable statements about prehistoric technology. Technologists recognise that any reduction process is subject to a large number of extraneous variables. It has been noted that reduction is necessarily dependent upon the size of the blanks manufactured for use (e.g. Kuhn, 1992, 1995b; Hiscock, 1984, 1994b; Dibble, 1995; Brantingham et al., 2000; Hiscock and Attenbrow, 2002); that different shaped blanks will give rise to different reduction processes (e.g. Villa, 1983; Van Peer, 1992; Bleed, 1996; Inizan et al., 1999; McPherron, 1999; Hiscock and Clarkson, 2007; see also Frison, 1968, p. 150); and that different reduction processes require different methods of measurement (e.g. Shott and Ballenger, 2007; Hiscock and Clarkson, 2005, 2007; Shott and Weedman, 2006; Jefferies, 1990; Kuhn, 1990). Likewise, the ability for certain blank morphologies to lose greater overall mass with successive resharpening episodes than others (Shott and Ballenger, 2007; Shott and Weedman, 2006), indicates that different levels of reduction may not, therefore, reflect different levels of use, but rather differences in the amount of reduction experienced by an artefact at each
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resharpening episode. In combination, these observations highlight the possibility that different shaped blanks and different types of reductive processes may also be accompanied by different rates of use and therefore different rates of reduction. The growing concern with the effect of blank morphology on artefacts’ capacity to resharpen is to be encouraged for its ability to enhance our understanding of archaeological assemblage variability; however the functional characteristics of blanks at the beginning of the use process and their effect on ongoing rejuvenation and resharpening processes have yet to be addressed. This paper seeks to complement current reduction theory by exploring the little understood relationship between the functional capacity of different shaped blanks and edge rejuvenation thresholds. 2. Experimental practice A highly controlled experimental program was conducted using 36 flakes made from Brandon Flint. All edges were used to scrape a single contact material, Baltic pine, a soft wood that had been oven seasoned prior to use in the experiments. In order to isolate the specific effects of the individual variables being tested and avoid including the effects of any uncontrolled variables in the data produced, experimentation was mechanised using a machine designed by the Department of Engineering at the Australian National University, purpose built for testing transverse motions. Built into the machine was the ability to control the length and speed of the stroke and an inbuilt feed mechanism on the table which allowed the contact material attached to the table to be moved along at a constant increment, always providing a fresh workable surface for the implement. A holding device for the artefacts themselves enabled the relief-angle to be controlled as well as the downwards pressure on the artefact. The number of strokes performed by each artefact was recorded by an electronic panel designed to disconnect contact between the material and working edge at the end of each use period (see Collins, 2007 for full details of the machine used). Mechanisation ensured that experiments were conducted in the same way and that results were therefore comparable. All experiments were conducted on unretouched, decorticated flakes which, along with speed, pressure, contact surface, stroke length, contact material and action were held constant throughout. This allowed edge shape, edge angle and the duration of use to be varied and the individual effects of each to be isolated and quantified. Edge shape was determined relative to points of contact between the flat timber worked and the functional edge. On convex edges, contact between the working material and the edge occurred at the central point of the convexity. Conversely, concave edges made contact with the worked material at either side of the concavity, while straight edges showed a consistent length of contact between material and edge along a length exceeding 14 mm (see Fig. 1). Edge angles were required to fall within one or other of two categories; high (60e65 degrees) or low (20e25 degrees). Measurements were taken at each of 3 points along
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Fig. 1. Points of contact for concave, convex and straight edges respectively. Where force is constant, the pressure resulting on each of these edges will differ considerably with contact area.
enabled the statistical verification of results through the replication of experiments. Twelve experiments were conducted with each of the three edge shapes tested; six involved high edge angles and six involved low edge angles. Each combination of edge shape and angle was therefore used in an identical fashion six times, giving greater confidence in the results generated (see Fig. 2). 3. Use effectiveness for different edge morphologies
the working edge, using a goniometer, and were required to fall into the 5 degree range of either high or low edge angle categories at each of the three points in order to qualify for that edge angle category. Stroke number was used to measure the amount of use performed by each artefact. All scraping activities were unidirectional, with the artefact lifted from the wood at the end of each stroke and contact re-established at the beginning of the next stroke. A feed mechanism on the machine allowed the artefact to move at a set increment of 2 mm across the wood with each stroke, which meant that a new area of timber was worked with each stroke. Due to the ability to control all other use related variables through the mechanisation of the use process, edge performance was able to be simply measured by weighing the amount of wood removed by the artefact edge in each particular stroke run. For every experiment, weights were taken for both the artefact and the contact material at the beginning and end of each use interval. Measurements were taken at 200 stroke intervals up to a maximum of 2400 strokes. Material loss represents just one of a number of possible measures of artefact performance and factors other than volume of material removed are likely to affect the decision to utilise one edge over another. For example, qualitative considerations such as the fineness of the work required may mean that convex or concave edges (producing a single or double groove respectively) are undesirable in some cases. However, for the purposes of this study, material loss is a valid criterion for quantitatively assessing whether differences in edge morphology translate to differences in performance and rejuvenation rates. Alternative measures of performance should be explored in future studies. Artefact edges were not retouched at any stage in the experiment. For consistency, all artefacts were used for a minimum of 1200 strokes regardless of how effective the edge was throughout each interval. In order to record the long-term usability of particular edges, an arbitrarily defined minimum performance level was established for analytical convenience, beyond which material losses were insufficient to justify the time and effort expended. In this study, the point at which an edge failed to remove more than 0.5 g of wood in each of three successive 200 stroke use intervals was regarded, for the purpose of modelling, as the point at which the artefact would no longer survive in a prehistoric use context without modification. Those artefacts that continued to be used for an entire run of 2400 strokes were those with the greatest ability to maintain their level of performance over longer term use. The level of control exacted over this experimental program
Two aspects of artefact performance were measured in this study. The first is a simple measure of effectiveness where the cumulative material losses are compared between edge morphologies. The second measure is of edge longevity or the amount of use an artefact is capable of providing before being discarded or retouched (though no retouching was carried out in this experiment), measured here in use durations of 200 strokes. Artefacts will necessarily differ in the amounts of material they are able to remove in accordance with duration of use; those artefacts used for longer are likely to have greater cumulative material loss than those used for only a short period of time. As such, measurements of performance must take into account both the overall effectiveness of the edge as well as its ability to maintain these performance levels over extended periods of time. To determine whether or not a particular edge plan had a higher likelihood of consistently strong levels of material loss over multiple use intervals, the data were analysed using survival analysis models. Survival models measure the probability that an artefact will be functional at a given time and identify whether or not particular variables are correlated with rates of survival or failure times (Lawless, 1982; Fox, 2002). Cox proportional hazard models were fitted to the data to examine which variables significantly influence artefact survival (longevity). Although just under 50% of the experimental edges failed during the study (see Table 1), neither edge plan nor edge angle were found to have a statistically significant effect on
Fig. 2. Material removed from a 200 stroke run with a concave edge plan.
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Table 1 Number of artefacts contributing to data points at each 200 stroke interval, relative to edge plan and angle Plan
Angle
Concave
High Low High Low High Low
Convex Straight
Duration (strokes)
Total
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
6 6 6 6 6 6 36
6 6 6 6 6 6 36
6 6 6 6 6 6 36
6 6 6 6 6 6 36
6 6 6 6 6 6 36
6 6 6 6 6 6 36
5 5 5 6 5 6 32
5 5 4 5 4 5 28
5 5 4 4 3 4 25
5 5 3 4 2 3 22
5 5 3 4 2 3 22
5 4 3 4 2 3 21
artefact survival, suggesting that artefact failure was either random, or not related, to the particular variables tested. Measurements of overall edge effectiveness in scraping soft wood, based on cumulative material loss over time, suggest greater complexity. Plots of material loss relative to each use interval for all edge plans and angles combined, illustrated in Fig. 3, indicate peak productivity occurred in the first 200 strokes. Despite minor fluctuations in material loss over time, a steady decline in productivity is evident from 200 strokes onwards. These results indicate that those edges capable of maintaining material losses sufficient to allow its continued use (that is, those that succeed in meeting minimum performance levels), show a constant rate of material loss over time. Statistical analyses of the individual effects of edge plan and angle on performance reveal distinct differences in productivity associated with edge morphology. In order to normalise the data for analysis, the log of cumulative material loss was used. The longitudinal nature of the data
(measurements taken every 200 strokes) meant that a linear mixed model could be fitted to the data using log10(cumulative material loss) as the response variable. The failure rates of artefacts after 1200 strokes mean that the data for the first 1200 strokes are more complete than for the following 1200 strokes. Consequently, statistical analyses were only conducted on the complete set of data up to 1200 strokes. The fitted means for log(cumulative material loss) according to each edge plan are plotted in Fig. 4. The point of least significant difference (lsd) is marked in the lower right corner of Fig. 4. Where the difference between two means is greater than the corresponding lsd, that difference is significant; the longer lsd relates to differences between the material losses of different edge plans in a single use duration, while the shorter lsd relates to significant differences in the performance of a single edge plan between use durations. The analyses revealed a highly significant affect of edge plan on performance over time ( p ¼ 0.003) and of edge angle ( p ¼ 0.010) with use. A significant difference in
100-1200 4.0 1.0
log (cumulative material loss)
95% CI Material Loss (g)
3.5
3.0
2.5
2.0
1.5
0.8
0.6
0.4
0.2 1.0
0.5
Plan=Concave Plan=Convex Plan=Straight
00 12 00 14 00 16 00 18 00 20 00 22 00 24 00
0 80
10
0
60 0
40
20 0
0.0 200
400
600
800
lsd
1000
1200
Duration
Duration (Strokes) Fig. 3. Mean material loss per use interval generated by edges used to scrape soft wood.
Fig. 4. Predicted log10(cumulative material loss) for interaction between edge plan and duration. Cumulative material loss refers to amount of wood removed by each edge plan.
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cumulative material loss exists between convex and straight plans, with this difference becoming greater with increased use. It is perhaps not surprising that the performance levels of concave edges fall between those of straight and convex edges. Concave edges will generally experience double the contact points of convex edges and less than half of that experienced by straight edges (depending upon their length). The affect of edge angle on performance is consistent with use duration, with low edge angles found to remove significantly more material than high edge angles (see Fig. 5). However, given that the affects of these two variables occur independently of one another, and not as part of an interaction between plan and edge angle, observed relationships between edge plans will retain regardless of the edge angle with which they are coupled. The two lsds illustrated in Fig. 4 predict significant differences between edge plans both during the same use interval (the larger lsd) and for the same edge plan in different intervals (the smaller lsd), showing differences over time and between edge plans. The value of utilising a convex plan in preference to a concave or straight alternative is therefore predicted to increase with use, with the least difference felt over short term uses and increasing to sizeable differences over longer use periods. Fig. 5 further indicates that a consistently higher level of productivity is also predicted to be possible by utilising a low edge angle where possible. Depending on the task to be performed, the decision to utilise one edge morphology over another is likely to have resulted in substantial differences in the time and energy required to complete it. While the results of these experiments relate specifically to the performance of unretouched edges, it is clear that they have important implications for broader reduction analyses and highlight a need for further research into this aspect of artefact function and reduction. 100-1200
log (cumulative material loss)
0.80
0.75
0.70
Isd
0.65
0.60
0.55
High
Low
Edge Angle Fig. 5. Predicted log10(cumulative material loss) for the affect of edge angle on performance irrespective of edge plan.
4. Discussion and conclusion These results reveal the existence of a strong relationship between artefact performance and blank morphology. The ability for differences in edge plan and angle to result in significantly different levels of material loss suggests that use effectiveness fluctuated with blank morphology, with different specimens capable of achieving greater performance levels or longer use lives than others. Of greater value are the implications that performance differences have for reduction analyses. The first of these is the challenge it poses to the principle of proportionality between retouch and amount of use implied in reduction measures. A straight edge is able to remove in 800 strokes a cumulative material loss equivalent to that produced by a convex edge of equivalent angle in almost half the time (Fig. 4). Even in the first 200 strokes, convex edges are capable of removing 25% more material than straight edges e an advantage that increases in magnitude with each use interval. For that reason, a straight edge is predicted to require a higher frequency of rejuvenation to achieve similar levels of productivity as those achieved by a convex edge. As such, a far greater amount of retouch is likely to be exhibited by a straight edge than an alternative used in a similar way for an equivalent amount of time. The key implication here is that equivalent levels of reduction cannot be assumed to indicate equivalent rates of use, with reduction rates likely to differ both with use and with the suitability of the blank morphology to the function required of it. The second implication is the challenge it imposes to ongoing measurements of reduction. At present, technologists acknowledge blank size, raw material quality, amount of use and type of reduction as primary determinants of artefact form and degree of reduction exhibited at discard. However, these results suggest even greater complexity is involved, with the type of use and the morphology of the blank dictating the point at which reduction may first be required, the rate at which it must re-occur to maintain performance levels and, to some extent, whether or not rejuvenation will occur in the first place. Technologists must now seek new techniques for measuring artefact reduction that are able to incorporate these greater complexities. The results presented here were limited to tests of only two morphological variables, one action and one contact material. It seems inevitable that even greater complexity is to be expected from testing a wider range of morphological variables, functions and contact materials. In addition, the decision to stop using each edge after 2400 strokes meant that several of the edges were not exhausted at the end of the experiment and were capable of further use. As such, it is not possible to quantify rates of material loss beyond this duration or to determine the final point at which the edge ceases to be effective. Likewise, no attempt was made to quantify the effects of retouch on edge performance which is also likely to impact greatly on rates of rejuvenation by changing the morphology of the blank with each retouch episode. Future research into the effects of a wider range of morphological and use variables on artefact performance must
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therefore become a priority in future research if we are to understand the complex range of interacting variables contributing to artefact reduction and diversity in stone artefact assemblages. Acknowledgements Many thanks to Robert Gresham, Joel Gresham and Ben Nash at the Department of Engineering, Australian National University, for the manufacture of machine used to conduct the experiments detailed in this paper. Thanks also to Tom Fuller for providing the flint flakes used in experimentation. I would also like to thank Peter Hiscock, Michael Shott, Ben Marwick and two anonymous reviewers for reading and commenting on earlier drafts of this paper. This research was supported by the Centre for Archaeological Research at the Australian National University. References Ahler, S.A., 1971. Projectile form and function at the Rogers Rock Shelter, Missouri. Missouri Archaeological Society Research Series No. 8. Missouri Archaeological Society, Columbia, MO. Baulmer, M., 1888. Core reduction, flake production, and the Middle Palaeolithic industry of Zobiste (Yugoslavia). In: Dibble, H.L., Monet-White, A. (Eds.), Upper Pelistocene Prehistory of Western Eurasia. University of Pennsylvania, Philadelphia, PA, pp. 255e274. Bietta, A., Grimaldi, S., 1990e1991. Patterns of reduction sequences at Grotta Breuil: statistical analyses and comparisons of archaeological vs experimental data. In: Fossil Man of Monte Circeo: Fifty Years of Studies on the Neandertals in Latium. Istituto Italiano di Paleontologia Umana, Rome, pp. 379e406. Bisson, M., 2000. Nineteenth century tools for twenty-first century archaeology? Why the middle paleolithic typology of Francois Bordes must be replaced. Journal of Archaeological Method and Theory 7 (1), 1e48. Bleed, P., 1996. Risk and cost in Japanese microcore technology. Lithic Technology 21, 95e107. Bleed, P., 2001. Trees or chains, links or branches: conceptual alternatives for consideration of stone tool production and other sequential activities. Journal of Archaeological Method and Theory 8 (1), 101e127. Bleed, P., 2002. Cheap, regular and reliable: implications of design variation in Late Pleistocene Japanese microblade technology. In: Elston, R.G., Kuhn, S.L. (Eds.), Thinking Small: Global Perspectives on Microlitholization. Archaeological Papers, No 12. The American Anthropological Association, pp. 95e102. Boe¨da, E., 1995. Levallois: a volumetric construction, methods, a technique. In: Dibble, H., Bar-Yosef, O. (Eds.), The Definition and Interpretation of Levallois Technology. Prehistory Press, Madison, pp. 41e68. Brantingham, P.J., Olsen, J.W., Rech, J.A., Krivoshapkin, A.I., 2000. Raw material quality and prepared core technologies in Northeast Asia. Journal of Archaeological Science 27, 255e274. Clarkson, C., 2002a. Holocene scraper reduction, Technological organization and landuse at Ingaladdi Rockshelter, Northern Australia. Archaeology in Oceania 37 (2), 79e86. Clarkson, C., 2002b. An index of invasiveness and archaeological verification. Journal of Archaeological Science 61, 65e75. Clarkson, C., 2005. Tenuous types: ‘scraper’ reduction continuums in Wardaman Country, Northern Australia. In: Clarkson, C., Lamb, L. (Eds.), Lithics ’Down Under’: Australian Approaches to Lithic ReductionUse and ClassificationBritish Archaeological Reports International Monograph Series S1408. Archaeopress, Oxford. Collins, S., 2007. An experimental evaluation of the principles and frameworks for interpreting the function of archaeological stone artefacts. Unpublished PhD thesis, Australian National University.
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McPherron, S.P., 2003. Typological and technological variability in the bifaces from Tabun Cave, Israel. In: Soressi, M., Dibble, H. (Eds.), From Prehistoric Bifaces to Human Behaviour: Multiple Approaches to the Study of Bifacial Technology. University of Pennsylvania Museum Press, Philadelphia, PA, pp. 55e75. Morrow, J., 1997. End scraper morphology and use-life: an approach for studying Paleoindian lithic technology and mobility. Lithic Technology 22, 70e85. Neeley, M., Barton, C., 1994. A new approach to interpreting late Pleistocene microlithic industries in southwest Asia. Antiquity 68, 275e288. Rolland, N., Dibble, H.L., 1990. A new synthesis of Middle Paleolithic assemblage variability. American Antiquity 55, 480e499. Shott, M.J., 1995. How much is a scraper? Curation, use rates and the formation of scraper assemblages. Lithic Technology 20, 52e72. Shott, M.J., 1996. Stage versus continuum in the debris assemblage from production of a fluted biface. Lithic Technology 21, 6e22. Shott, M.J., Ballenger, J.A.M., 2007. Biface reduction and the measurement of Dalton curation: a Southeastern United States case study. American Antiquity 72 (1), 153e175. Shott, M.J., Weedman, K.J., 2006. Measuring reduction in stone tools: an ethnoarchaeological study of Gamo hidescrapers from Ethiopia. Journal of Archaeological Science 34, 1016e1035. Van Peer, P., 1992. The Levallois Reduction Strategy. Monographs in World Archaeology No 13. Prehistory Press, Wisconsin. Villa, P., 1983. Terra Amata and the Middle Pleistocene Archaeological Record of Southern France. University of California Press, Berkeley, CA.
Experimental investigations into edge performance and its implications for stone artefact reduction modelling Sophie Collins* Department of Archaeology and Natural History, Research School of Pacific and Asian Studies, Australian National University, Coombs Building 9, Fellows Road, ACT 0200, Australia Received 28 November 2007; received in revised form 21 January 2008; accepted 22 January 2008
Abstract This paper details an experimental investigation into stone artefact performance and use, and examines the implications for maintenance and rejuvenation activities. Controlled experiments testing the performance of differently shaped working edges reveal that rates of use attrition are not constant; they are dependent upon the blank morphology’s suitability to particular tasks. The evidence contributes to a broader understanding of the principles of reduction analyses by showing that morphological differences in blanks are accompanied by differences in the artefacts’ functional capacity. These differences in turn affect the rate at which maintenance and rejuvenation activities will be required and therefore the extent of reduction exhibited at discard. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Lithics; Experimentation; Performance; Use; Reduction
1. Reduction analysis Lithic technologists emphasise the reductive process as a means of understanding technological variability in the archaeological record (Villa, 1983; Dibble, 1984, 1987, 1995; Van Peer, 1992; Hiscock, 1993, 1994b, 1996a,b, 2006; Boe¨da, 1995; Shott, 1996; Bisson, 2000; Bleed, 1996, 2001; Hiscock and Attenbrow, 2002; Clarkson, 2002a). The processes of edge rejuvenation and maintenance in stone artefacts result in the essential properties of size, mass and form changing and reducing with successive rejuvenation events (Shott and Weedman, 2006). In most cases, the morphology of an artefact at discard is argued to indicate the amount of reduction the artefact has sustained, with some forms represented by earlier stages of reduction and others by more intensively reduced forms along a continuum of reduction (e.g. Goodyear, 1974; Jelinek, 1976; Villa, 1983; Baulmer, 1888; Hiscock, 1994b; Dibble, 1984, 1987, 1995; Hoffman, 1985; Flenniken and * Tel.: þ61 414306762. E-mail address: [email protected] 0305-4403/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2008.01.017
Raymond, 1986; Holdaway et al., 1996; Hiscock and Attenbrow, 2002). Substantial work has now been done on both the development of accurate measures of reduction (e.g. Shott and Ballenger, 2007; Hiscock and Clarkson, 2005, 2007; Shott and Weedman, 2006; Jefferies, 1990; Kuhn, 1990) and the characterisation of reduction sequences for artefact classes found all over the world (e.g. Australia, Hiscock and Veth, 1991; Hiscock, 1993, 1994a, 1998, 2003; Clarkson, 2002a; Hiscock and Attenbrow, 2002; Libya, Hiscock, 1996b; south west Asia, Neeley and Barton, 1994; Japan, Bleed, 1996, 2002; Yugoslavia, Baumler, 1888; North America, Goodyear, 1974; Hoffman, 1985; Morrow, 1997; Israel, Marks and Volkman, 1983; Gordon, 1993; McPherron, 2003; Egypt, van Peer 1992; Europe, Bietta and Grimaldi, 1990e1991; Italy, Kuhn, 1992; and in particular France, Villa, 1983; Dibble, 1984, 1987, 1995; Rolland and Dibble, 1990; Kuhn, 1995a; Holdaway et al., 1996). However, while quantifying amounts of reduction has received some attention, the idea that different shaped blanks and different types of reduction may be accompanied by different rates of use and therefore different rates of reduction, is yet to be examined.
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This paper explores this aspect of reduction by describing the results of controlled experimentation showing how artefact use influences edge rejuvenation on three blank morphologies. Artefact function is intimately related to retouch by dictating the point at which retouch/resharpening is required and whether or not it is necessary at all. The greater the amount of work an edge is able to sustain, the lower the frequency of retouch required, and the longer its use life. Data on the effectiveness of various functional edges in performing particular tasks is therefore necessary to allow some understanding of how much use may be reflected by a particular stage of reduction. The goal of this paper is to determine whether different blank forms have different performance characteristics; which would in turn imply that artefact reduction rates are influenced both by blank form and use rates. The idea of retouch as resharpening necessarily equates retouch with use; the more heavily an artefact has been reduced, the greater the amount of use attributed to it. This point has been illustrated by many studies calculating the reduction sequences for traditional archaeological ‘types,’ in which the type of each class of artefact represented at discard is argued to be subject to the amount of reduction the artefact has sustained e through use (e.g. North American and Australian projectile point typologies, Ahler, 1971; Hoffman, 1985; Hiscock, 1994b; Flenniken and Raymond, 1986; bifacial handaxes, Jones, 1994; McPherron, 1995, 1999; notched tools, Holdaway et al., 1996; and additional scraper types, Shott, 1995; Morrow, 1997; Clarkson, 2002b, 2005). Importantly, in order to allow comparisons between different artefact morphologies and the amount of reduction evidenced, the relationship between use and retouch is assumed to be fixed. This has allowed artefacts exhibiting equivalent amounts of retouch to be attributed with similar amounts of use and means the technologist need only identify reduction intensity at a site to also understand use intensity. Rates of use and reduction are assumed to be constant; however this constancy is yet to be demonstrated, representing a gap in the knowledge required for making reliable statements about prehistoric technology. Technologists recognise that any reduction process is subject to a large number of extraneous variables. It has been noted that reduction is necessarily dependent upon the size of the blanks manufactured for use (e.g. Kuhn, 1992, 1995b; Hiscock, 1984, 1994b; Dibble, 1995; Brantingham et al., 2000; Hiscock and Attenbrow, 2002); that different shaped blanks will give rise to different reduction processes (e.g. Villa, 1983; Van Peer, 1992; Bleed, 1996; Inizan et al., 1999; McPherron, 1999; Hiscock and Clarkson, 2007; see also Frison, 1968, p. 150); and that different reduction processes require different methods of measurement (e.g. Shott and Ballenger, 2007; Hiscock and Clarkson, 2005, 2007; Shott and Weedman, 2006; Jefferies, 1990; Kuhn, 1990). Likewise, the ability for certain blank morphologies to lose greater overall mass with successive resharpening episodes than others (Shott and Ballenger, 2007; Shott and Weedman, 2006), indicates that different levels of reduction may not, therefore, reflect different levels of use, but rather differences in the amount of reduction experienced by an artefact at each
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resharpening episode. In combination, these observations highlight the possibility that different shaped blanks and different types of reductive processes may also be accompanied by different rates of use and therefore different rates of reduction. The growing concern with the effect of blank morphology on artefacts’ capacity to resharpen is to be encouraged for its ability to enhance our understanding of archaeological assemblage variability; however the functional characteristics of blanks at the beginning of the use process and their effect on ongoing rejuvenation and resharpening processes have yet to be addressed. This paper seeks to complement current reduction theory by exploring the little understood relationship between the functional capacity of different shaped blanks and edge rejuvenation thresholds. 2. Experimental practice A highly controlled experimental program was conducted using 36 flakes made from Brandon Flint. All edges were used to scrape a single contact material, Baltic pine, a soft wood that had been oven seasoned prior to use in the experiments. In order to isolate the specific effects of the individual variables being tested and avoid including the effects of any uncontrolled variables in the data produced, experimentation was mechanised using a machine designed by the Department of Engineering at the Australian National University, purpose built for testing transverse motions. Built into the machine was the ability to control the length and speed of the stroke and an inbuilt feed mechanism on the table which allowed the contact material attached to the table to be moved along at a constant increment, always providing a fresh workable surface for the implement. A holding device for the artefacts themselves enabled the relief-angle to be controlled as well as the downwards pressure on the artefact. The number of strokes performed by each artefact was recorded by an electronic panel designed to disconnect contact between the material and working edge at the end of each use period (see Collins, 2007 for full details of the machine used). Mechanisation ensured that experiments were conducted in the same way and that results were therefore comparable. All experiments were conducted on unretouched, decorticated flakes which, along with speed, pressure, contact surface, stroke length, contact material and action were held constant throughout. This allowed edge shape, edge angle and the duration of use to be varied and the individual effects of each to be isolated and quantified. Edge shape was determined relative to points of contact between the flat timber worked and the functional edge. On convex edges, contact between the working material and the edge occurred at the central point of the convexity. Conversely, concave edges made contact with the worked material at either side of the concavity, while straight edges showed a consistent length of contact between material and edge along a length exceeding 14 mm (see Fig. 1). Edge angles were required to fall within one or other of two categories; high (60e65 degrees) or low (20e25 degrees). Measurements were taken at each of 3 points along
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Fig. 1. Points of contact for concave, convex and straight edges respectively. Where force is constant, the pressure resulting on each of these edges will differ considerably with contact area.
enabled the statistical verification of results through the replication of experiments. Twelve experiments were conducted with each of the three edge shapes tested; six involved high edge angles and six involved low edge angles. Each combination of edge shape and angle was therefore used in an identical fashion six times, giving greater confidence in the results generated (see Fig. 2). 3. Use effectiveness for different edge morphologies
the working edge, using a goniometer, and were required to fall into the 5 degree range of either high or low edge angle categories at each of the three points in order to qualify for that edge angle category. Stroke number was used to measure the amount of use performed by each artefact. All scraping activities were unidirectional, with the artefact lifted from the wood at the end of each stroke and contact re-established at the beginning of the next stroke. A feed mechanism on the machine allowed the artefact to move at a set increment of 2 mm across the wood with each stroke, which meant that a new area of timber was worked with each stroke. Due to the ability to control all other use related variables through the mechanisation of the use process, edge performance was able to be simply measured by weighing the amount of wood removed by the artefact edge in each particular stroke run. For every experiment, weights were taken for both the artefact and the contact material at the beginning and end of each use interval. Measurements were taken at 200 stroke intervals up to a maximum of 2400 strokes. Material loss represents just one of a number of possible measures of artefact performance and factors other than volume of material removed are likely to affect the decision to utilise one edge over another. For example, qualitative considerations such as the fineness of the work required may mean that convex or concave edges (producing a single or double groove respectively) are undesirable in some cases. However, for the purposes of this study, material loss is a valid criterion for quantitatively assessing whether differences in edge morphology translate to differences in performance and rejuvenation rates. Alternative measures of performance should be explored in future studies. Artefact edges were not retouched at any stage in the experiment. For consistency, all artefacts were used for a minimum of 1200 strokes regardless of how effective the edge was throughout each interval. In order to record the long-term usability of particular edges, an arbitrarily defined minimum performance level was established for analytical convenience, beyond which material losses were insufficient to justify the time and effort expended. In this study, the point at which an edge failed to remove more than 0.5 g of wood in each of three successive 200 stroke use intervals was regarded, for the purpose of modelling, as the point at which the artefact would no longer survive in a prehistoric use context without modification. Those artefacts that continued to be used for an entire run of 2400 strokes were those with the greatest ability to maintain their level of performance over longer term use. The level of control exacted over this experimental program
Two aspects of artefact performance were measured in this study. The first is a simple measure of effectiveness where the cumulative material losses are compared between edge morphologies. The second measure is of edge longevity or the amount of use an artefact is capable of providing before being discarded or retouched (though no retouching was carried out in this experiment), measured here in use durations of 200 strokes. Artefacts will necessarily differ in the amounts of material they are able to remove in accordance with duration of use; those artefacts used for longer are likely to have greater cumulative material loss than those used for only a short period of time. As such, measurements of performance must take into account both the overall effectiveness of the edge as well as its ability to maintain these performance levels over extended periods of time. To determine whether or not a particular edge plan had a higher likelihood of consistently strong levels of material loss over multiple use intervals, the data were analysed using survival analysis models. Survival models measure the probability that an artefact will be functional at a given time and identify whether or not particular variables are correlated with rates of survival or failure times (Lawless, 1982; Fox, 2002). Cox proportional hazard models were fitted to the data to examine which variables significantly influence artefact survival (longevity). Although just under 50% of the experimental edges failed during the study (see Table 1), neither edge plan nor edge angle were found to have a statistically significant effect on
Fig. 2. Material removed from a 200 stroke run with a concave edge plan.
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Table 1 Number of artefacts contributing to data points at each 200 stroke interval, relative to edge plan and angle Plan
Angle
Concave
High Low High Low High Low
Convex Straight
Duration (strokes)
Total
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
6 6 6 6 6 6 36
6 6 6 6 6 6 36
6 6 6 6 6 6 36
6 6 6 6 6 6 36
6 6 6 6 6 6 36
6 6 6 6 6 6 36
5 5 5 6 5 6 32
5 5 4 5 4 5 28
5 5 4 4 3 4 25
5 5 3 4 2 3 22
5 5 3 4 2 3 22
5 4 3 4 2 3 21
artefact survival, suggesting that artefact failure was either random, or not related, to the particular variables tested. Measurements of overall edge effectiveness in scraping soft wood, based on cumulative material loss over time, suggest greater complexity. Plots of material loss relative to each use interval for all edge plans and angles combined, illustrated in Fig. 3, indicate peak productivity occurred in the first 200 strokes. Despite minor fluctuations in material loss over time, a steady decline in productivity is evident from 200 strokes onwards. These results indicate that those edges capable of maintaining material losses sufficient to allow its continued use (that is, those that succeed in meeting minimum performance levels), show a constant rate of material loss over time. Statistical analyses of the individual effects of edge plan and angle on performance reveal distinct differences in productivity associated with edge morphology. In order to normalise the data for analysis, the log of cumulative material loss was used. The longitudinal nature of the data
(measurements taken every 200 strokes) meant that a linear mixed model could be fitted to the data using log10(cumulative material loss) as the response variable. The failure rates of artefacts after 1200 strokes mean that the data for the first 1200 strokes are more complete than for the following 1200 strokes. Consequently, statistical analyses were only conducted on the complete set of data up to 1200 strokes. The fitted means for log(cumulative material loss) according to each edge plan are plotted in Fig. 4. The point of least significant difference (lsd) is marked in the lower right corner of Fig. 4. Where the difference between two means is greater than the corresponding lsd, that difference is significant; the longer lsd relates to differences between the material losses of different edge plans in a single use duration, while the shorter lsd relates to significant differences in the performance of a single edge plan between use durations. The analyses revealed a highly significant affect of edge plan on performance over time ( p ¼ 0.003) and of edge angle ( p ¼ 0.010) with use. A significant difference in
100-1200 4.0 1.0
log (cumulative material loss)
95% CI Material Loss (g)
3.5
3.0
2.5
2.0
1.5
0.8
0.6
0.4
0.2 1.0
0.5
Plan=Concave Plan=Convex Plan=Straight
00 12 00 14 00 16 00 18 00 20 00 22 00 24 00
0 80
10
0
60 0
40
20 0
0.0 200
400
600
800
lsd
1000
1200
Duration
Duration (Strokes) Fig. 3. Mean material loss per use interval generated by edges used to scrape soft wood.
Fig. 4. Predicted log10(cumulative material loss) for interaction between edge plan and duration. Cumulative material loss refers to amount of wood removed by each edge plan.
S. Collins / Journal of Archaeological Science 35 (2008) 2164e2170
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cumulative material loss exists between convex and straight plans, with this difference becoming greater with increased use. It is perhaps not surprising that the performance levels of concave edges fall between those of straight and convex edges. Concave edges will generally experience double the contact points of convex edges and less than half of that experienced by straight edges (depending upon their length). The affect of edge angle on performance is consistent with use duration, with low edge angles found to remove significantly more material than high edge angles (see Fig. 5). However, given that the affects of these two variables occur independently of one another, and not as part of an interaction between plan and edge angle, observed relationships between edge plans will retain regardless of the edge angle with which they are coupled. The two lsds illustrated in Fig. 4 predict significant differences between edge plans both during the same use interval (the larger lsd) and for the same edge plan in different intervals (the smaller lsd), showing differences over time and between edge plans. The value of utilising a convex plan in preference to a concave or straight alternative is therefore predicted to increase with use, with the least difference felt over short term uses and increasing to sizeable differences over longer use periods. Fig. 5 further indicates that a consistently higher level of productivity is also predicted to be possible by utilising a low edge angle where possible. Depending on the task to be performed, the decision to utilise one edge morphology over another is likely to have resulted in substantial differences in the time and energy required to complete it. While the results of these experiments relate specifically to the performance of unretouched edges, it is clear that they have important implications for broader reduction analyses and highlight a need for further research into this aspect of artefact function and reduction. 100-1200
log (cumulative material loss)
0.80
0.75
0.70
Isd
0.65
0.60
0.55
High
Low
Edge Angle Fig. 5. Predicted log10(cumulative material loss) for the affect of edge angle on performance irrespective of edge plan.
4. Discussion and conclusion These results reveal the existence of a strong relationship between artefact performance and blank morphology. The ability for differences in edge plan and angle to result in significantly different levels of material loss suggests that use effectiveness fluctuated with blank morphology, with different specimens capable of achieving greater performance levels or longer use lives than others. Of greater value are the implications that performance differences have for reduction analyses. The first of these is the challenge it poses to the principle of proportionality between retouch and amount of use implied in reduction measures. A straight edge is able to remove in 800 strokes a cumulative material loss equivalent to that produced by a convex edge of equivalent angle in almost half the time (Fig. 4). Even in the first 200 strokes, convex edges are capable of removing 25% more material than straight edges e an advantage that increases in magnitude with each use interval. For that reason, a straight edge is predicted to require a higher frequency of rejuvenation to achieve similar levels of productivity as those achieved by a convex edge. As such, a far greater amount of retouch is likely to be exhibited by a straight edge than an alternative used in a similar way for an equivalent amount of time. The key implication here is that equivalent levels of reduction cannot be assumed to indicate equivalent rates of use, with reduction rates likely to differ both with use and with the suitability of the blank morphology to the function required of it. The second implication is the challenge it imposes to ongoing measurements of reduction. At present, technologists acknowledge blank size, raw material quality, amount of use and type of reduction as primary determinants of artefact form and degree of reduction exhibited at discard. However, these results suggest even greater complexity is involved, with the type of use and the morphology of the blank dictating the point at which reduction may first be required, the rate at which it must re-occur to maintain performance levels and, to some extent, whether or not rejuvenation will occur in the first place. Technologists must now seek new techniques for measuring artefact reduction that are able to incorporate these greater complexities. The results presented here were limited to tests of only two morphological variables, one action and one contact material. It seems inevitable that even greater complexity is to be expected from testing a wider range of morphological variables, functions and contact materials. In addition, the decision to stop using each edge after 2400 strokes meant that several of the edges were not exhausted at the end of the experiment and were capable of further use. As such, it is not possible to quantify rates of material loss beyond this duration or to determine the final point at which the edge ceases to be effective. Likewise, no attempt was made to quantify the effects of retouch on edge performance which is also likely to impact greatly on rates of rejuvenation by changing the morphology of the blank with each retouch episode. Future research into the effects of a wider range of morphological and use variables on artefact performance must
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therefore become a priority in future research if we are to understand the complex range of interacting variables contributing to artefact reduction and diversity in stone artefact assemblages. Acknowledgements Many thanks to Robert Gresham, Joel Gresham and Ben Nash at the Department of Engineering, Australian National University, for the manufacture of machine used to conduct the experiments detailed in this paper. Thanks also to Tom Fuller for providing the flint flakes used in experimentation. I would also like to thank Peter Hiscock, Michael Shott, Ben Marwick and two anonymous reviewers for reading and commenting on earlier drafts of this paper. This research was supported by the Centre for Archaeological Research at the Australian National University. References Ahler, S.A., 1971. Projectile form and function at the Rogers Rock Shelter, Missouri. Missouri Archaeological Society Research Series No. 8. Missouri Archaeological Society, Columbia, MO. Baulmer, M., 1888. Core reduction, flake production, and the Middle Palaeolithic industry of Zobiste (Yugoslavia). In: Dibble, H.L., Monet-White, A. (Eds.), Upper Pelistocene Prehistory of Western Eurasia. University of Pennsylvania, Philadelphia, PA, pp. 255e274. Bietta, A., Grimaldi, S., 1990e1991. Patterns of reduction sequences at Grotta Breuil: statistical analyses and comparisons of archaeological vs experimental data. In: Fossil Man of Monte Circeo: Fifty Years of Studies on the Neandertals in Latium. Istituto Italiano di Paleontologia Umana, Rome, pp. 379e406. Bisson, M., 2000. Nineteenth century tools for twenty-first century archaeology? Why the middle paleolithic typology of Francois Bordes must be replaced. Journal of Archaeological Method and Theory 7 (1), 1e48. Bleed, P., 1996. Risk and cost in Japanese microcore technology. Lithic Technology 21, 95e107. Bleed, P., 2001. Trees or chains, links or branches: conceptual alternatives for consideration of stone tool production and other sequential activities. Journal of Archaeological Method and Theory 8 (1), 101e127. Bleed, P., 2002. Cheap, regular and reliable: implications of design variation in Late Pleistocene Japanese microblade technology. In: Elston, R.G., Kuhn, S.L. (Eds.), Thinking Small: Global Perspectives on Microlitholization. Archaeological Papers, No 12. The American Anthropological Association, pp. 95e102. Boe¨da, E., 1995. Levallois: a volumetric construction, methods, a technique. In: Dibble, H., Bar-Yosef, O. (Eds.), The Definition and Interpretation of Levallois Technology. Prehistory Press, Madison, pp. 41e68. Brantingham, P.J., Olsen, J.W., Rech, J.A., Krivoshapkin, A.I., 2000. Raw material quality and prepared core technologies in Northeast Asia. Journal of Archaeological Science 27, 255e274. Clarkson, C., 2002a. Holocene scraper reduction, Technological organization and landuse at Ingaladdi Rockshelter, Northern Australia. Archaeology in Oceania 37 (2), 79e86. Clarkson, C., 2002b. An index of invasiveness and archaeological verification. Journal of Archaeological Science 61, 65e75. Clarkson, C., 2005. Tenuous types: ‘scraper’ reduction continuums in Wardaman Country, Northern Australia. In: Clarkson, C., Lamb, L. (Eds.), Lithics ’Down Under’: Australian Approaches to Lithic ReductionUse and ClassificationBritish Archaeological Reports International Monograph Series S1408. Archaeopress, Oxford. Collins, S., 2007. An experimental evaluation of the principles and frameworks for interpreting the function of archaeological stone artefacts. Unpublished PhD thesis, Australian National University.
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